The phase equilibria in the system NaF–AlF₃–CaF₂ were studied at sodium and aluminum fluorides molar ratio equal to 1.17. This composition is eutectic with a melting point of 680°С. The thermal analysis, DSC and XRD methods were used. Samples were prepared from individual salts. Aluminum fluoride was purified from oxygen-containing impurities by ammonium fluoride in a glassy carbon crucible. For XRD and DSC, the melt was frozen on an alundum stick to obtain hardened samples. Liquidus temperatures were obtained by recording cooling curves in thermo-EMF – time coordinates using an APPA 502 multimeter. Solidus temperatures were studied using a STA 449C Jupiter synchronous heat analyzer (NETZSCH, Germany). A Rigaku MiniFlex 600 X-Ray diffractometer (Japan) with a copper anode was used for X-ray analysis. The XRD method allowed us to determine the phase composition of the samples. 7 samples were investigated. Calcium fluoride content ranged from 0 to 6.5 mol. %. The quasi-binary diagram of system (NaF–AlF₃)_eut–CaF₂ was obtained. The diagram has eutectic point with calcium fluoride content of 0.5 mol. % and temperature of 675°С. There are also two peritectic points on the diagram that correspond to the decomposition of complex compounds. The liquidus temperature after reaching the eutectic point increases sharply with calcium fluoride content, which results in the low solubility of CaF₂ in the low-melting eutectic NaF–AlF₃ at temperatures below 750°C. The data obtained are of interest for the development of technology for low-temperature electrolysis of aluminum.